If i try to install, i get an error "I'm sorry but you won't be able to install "Jaded's Blueplanet" because "FSO" is missing!"
Could you go into knossos settings > Knossos > and make sure you have "Show Engine Builds In Mod List" checked and click save. Then, under the Explore tab, find "FSO", click Details, and select "21.2.0" from the drop down at the upper left. You should either see a blue "Update" or a blue "Install" button.
Please let me know which one it shows for you. And if it shows the install button go ahead and install FSO 21.2.0, that should resolve your issue.
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The current release of Blueplanet does not work on FSO 21.4.0, so 21.2.0 is required instead. Jaded's BPC enforces this restriction and, apparently, knossos doesn't handle that well.